The invention relates to a motor vehicle drive arrangement with a gear mechanism having a variable transmission ratio and an oil pump for providing pressurized oil to the gear mechanism for operating shifting elements and an electric motor for driving the oil pump.
DE 199 23 154 A1 discloses a motor vehicle drive arrangement of this type in which an oil pump is connected to an electric motor via a freewheeling mechanism, and to a traveling drive train via another freewheeling mechanism. As a result, the oil pump is driven either by the electric motor or the traveling drive train as a function of the rotational speed. Only a very small amount of installation space is available in the engine cavity of motor vehicles so that it is difficult to accommodate the two freewheeling mechanisms and the electric motor.
In practice, motor vehicle drive devices are known whose travel drive train (motor vehicle drive train) includes an internal combustion engine and an automatic transmission arranged axially one behind the other, with the automatic transmission containing a hydrodynamic torque converter and a mechanical drive gear mechanism which contains planetary gearwheel sets and shifting elements for shifting the planetary gearwheel sets. The torque converter is located axially between the internal combustion engine and the mechanical drive gear mechanism. In order to operate the shifting elements (clutches and/or shifting brakes) and in order to cool the mechanical drive gear mechanism and to supply oil to the torque converter, an oil pump is provided which can be driven by the vehicle travel drive train via a mechanical drive connection. The oil pump is located axially between the torque converter and the mechanical drive gear mechanism, and surrounds a drive shaft.
Because of increasing demands to reduce fuel consumption and emissions, in future it will be necessary to adopt a start/stop operating mode of an internal combustion engine, for example at traffic lights in towns. In order to start the internal combustion engine conveniently, suitable starter/generators and various hybrid systems (travel drive systems containing at least two different drive motors, for example an internal combustion engine and at least one electric motor) have been developed.
The oil pump of the known automatic transmissions is driven by means of the pump wheel of the torque converter, which wheel is coupled permanently to the crankshaft of the internal combustion engine. As a result, when the internal combustion engine is shut down the oil pump cannot be driven so that, when the internal combustion engine is shut down, the oil pressure needed to operate the shifting elements (clutches and possibly shifting brakes) and also for lubrication cannot be maintained. As a result, it is not possible to start up the motor vehicle again quickly after the internal combustion engine has stopped. When starting up the motor vehicle it is then necessary to wait, after the internal combustion engine has started, until the oil system of the automatic transmission has been filled and a sufficiently high oil pressure level has built up in order to activate the shifting elements. This is very inconvenient under certain conditions and potentially dangerous. The requirement for convenience could be satisfied by driving the oil pump in accordance with the abovementioned DE 199 23 154 A1 or by providing an additional oil pump which is driven, when required, by an electric motor in order to maintain the oil supply and the oil pressure while the internal combustion engine is shut down. However, both solutions fail in most motor vehicles due to the fact that there is not sufficient installation space available in them and/or the existing components of the motor vehicle drive train would have to be changed, which would be very expensive and would also prevent series manufacture of different vehicles using identical components or identical assemblies.
It is the object of the invention to provide a drive arrangement, in particular for passenger cars, in such a way that the amount of oil which is necessary to start up and drive the motor vehicle and the oil pressure which is necessary for this purpose is present in the motor vehicle drive gear mechanism immediately after the vehicle drive unit, which may be an internal combustion engine or an electric motor or some other type of motor, is started, without the need for significant installation space. This object should be achieved in such a way that the arrangement can also be used for various types of known vehicles which are series-manufactured, without requiring a large degree of technical complexity or financial expenditure.